1. Field of the Invention
The present invention relates generally to chemical-mechanical planarization (CMP) systems, and more particularly, to methods and systems for applying one or more liquids to the CMP polishing pad.
2. Description of the Related Art
Semiconductor devices are typically formed on semiconductor substrates by forming multiple layers, one over another, to create multi-level structures. Because the multiple layers are formed over one another, a surface topography of the wafer can become irregular. An uncorrected irregularity can increase with subsequent layers. Chemical mechanical planarization (CMP) is a fabrication process used to planarize the surface of a semiconductor wafer so as to remove the topographical irregularities. CMP can also be used to perform additional fabrication processes including polishing, buffing, cleaning, etching, and the like. CMP can also include cleaning, buffing, polishing, planarizing, and otherwise processing substrates used in such applications as flat panel displays, hard disks, and the like.
In general, CMP processes include holding and rotating of a substrate against a preparation surface (i.e., the surface of a polishing pad) under a controlled pressure. Typical CMP apparatus include linear belt processing systems in which a continuous loop belt having a preparation surface is supported between two or more drums or rollers. The drums move the belt through a rotary path presenting a flat preparation surface against which the substrate is applied. Typically, the substrate is supported and rotated by a carrier (i.e., polishing head) and a polishing platen may be located on the underside of the belt. The platen provides a stable surface over which the belt travels, and the substrate is applied to the preparation surface of the belt against the stable surface provided by the platen.
A CMP apparatus can also include rotary CMP processing tools having a circular pad configuration for the preparation surface, orbital CMP processing tools similar to the circular CMP processing tool, sub-aperture CMP processing tools, and other CMP processing tools and systems providing multiple configurations that, in general, utilize friction to planarize, polish, buff, clean, or otherwise process the surface of a substrate such as a semiconductor wafer having integrated circuits or other structures fabricated thereon.
CMP processing typically includes the use of one or more and even varying combinations of abrasives, chemistries, rinsing or cleaning fluids, and the like to maximize effective use of friction for substrate preparation. Abrasives are often suspended in an aqueous solution, known as slurry, and deposited on the preparation surface. In some configurations, abrasives are provided as a part of the preparation surface and are known as fixed abrasive configurations.
FIG. 1A shows a typical linear belt CMP processing system 10. The linear belt CMP processing system 10 includes a wafer 12 applied against a linear processing belt 14. The wafer 12 is attached to a carrier 16 and can rotate the wafer 12 and to apply the wafer 12 against the linear processing belt 14 with a force 18. A platen 22 can provide a stable and secure surface against which the wafer 12 and linear processing belt 14 are supported. Linear processing belt 14 is positioned on and around two drums 20 providing support and rotation to linear processing belt 14. A single point slurry dispensing apparatus 26 dispenses slurry 24 “upstream” from wafer 12 so that the belt 14 can carry the slurry 24 to the wafer 12.
FIG. 1B shows an alternative slurry dispensing system. The alternative slurry dispensing system includes a slurry manifold 30, which is shown in an overhead view of a linear belt CMP processing system 10′. The slurry manifold 30 (i.e., a slurry bar) drips slurry through multiple dispensing outlets 32 across the width of the linear processing belt 14, upstream from wafer 12. One advantage of the slurry manifold 30 is that slurry can be dispensed across an entire width of preparation surface, or varying widths of a preparation surface depending on the number and spacing of slurry dispensing outlets 32 utilized, ensuring a complete coverage for multiple sizes of substrates.
One disadvantage to prior art slurry dispensing systems of either the single point or slurry manifold configurations is that the slurry is typically dispensed at flow rates of 100-200 cc/minute. As the slurry is an aqueous solution, slower flow rates (i.e., less than about 100 cc/minute) can allow for the solution to separate and/or not be distributed evenly across the slurry bar. Another disadvantage is that the slurry may only be dispensed from one or more slurry dispensing outlets and the droplets of slurry are dropped on the preparation surface at relative few locations. As a result, the slurry is not evenly applied across the width of the preparation surface.
Slurry and other process chemistries can also be very expensive. As a result, a higher process chemistry flow rates can equate to a higher CMP operating cost. In many CMP operations a slurry flow rate of less than about 100 cc/minute or less can provide equivalent results as a slurry flow rate of 200 cc/minute or more. However, the typical process chemistry dispensing systems cannot accurately and effectively dispense process chemistries at flow rates less than about 100 cc/minute. Excess process chemistries can also create an excessive waste byproduct stream. The excessive waste byproduct stream can further increase the operating cost due to the disposal and or recycling cost associated with the waste stream. What is needed is a system and method for evenly applying slurry and other process chemistries to the CMP preparation surface, at flow rates of about 100 cc/minute or less.
Another problem with conventional CMP systems is that CMP byproducts can build-up in the CMP preparation surface. By way of example, as the slurry and the preparation surface remove material from the wafer, the removed material and slurry are transported away from the wafer surface by pockets and crevices (i.e., pores) in the preparation surface. Often these pores can be relatively deep within the preparation surface. The CMP byproducts can contact or be re-deposited onto the surface of the wager when the preparation surface next contacts the wafer. The deposited CMP byproducts can also cause irregularities in the surface of the wafer such as particle contamination, scratches, gouges and other irregularities. In view of the foregoing, there is a need for a system and method for efficiently and effectively reducing or removing the CMP byproduct build-up from the preparation surface.